1. Field of the Invention
This invention relates to an optical unit used in a specimen analysis for the quantitative analysis of a specimen or a substance in the specimen such as a refractive index or an immunity measured value.
2. Description of Related Art
As a conventional specimen analyzer, there is the device that light of incident angles in a preset range including the angle of total reflection (hereinafter referred to as the preset convergent light) is rendered incident on a specimen placement section and the intensity of reflected light from the specimen placement section corresponding to each of the incident angles is detected so that an incident angle where the detected intensity is abruptly changed is detected.
For such a specimen analyzer, a device that, for example, the difference of the refractive index between substances is used to make an analysis is available. In this specimen analyzer, a specimen to be examined is placed at the specimen placement section consisting of a substance with a known refractive index. The preset convergent light is then rendered incident on the surface of the specimen placement section. At this time, light incident at an angle smaller than a critical angle ceases to undergo total reflection at the surface of the specimen placement section. By detecting the incident angle in this case, the refractive index of the specimen to be examined is determined and the physical properties of the specimen to be examined can be analyzed.
Also, for example, in a specimen analyzer utilizing the occurrence of surface plasmon, the specimen placement section is provided with a metal film on its surface. The specimen to be examined is placed on the metal film of the specimen placement section and the preset convergent light is rendered incident on the surface of the metal film. Here, when the light is incident at angles exceeding the critical angle, an evanescent wave having electric field distribution is produced at an interface between the metal film and the specimen to be examined. The surface plasmon is excited on the metal film by the evanescent wave. In addition, with respect to light incident at a particular incident angle, of light incident at the angles exceeding the critical angle, the evanescent wave and the surface plasmon cause wave number matching to bring about a resonance state. In this resonance state, the energy of light is transferred to the surface plasmon. As a result, in the light incident at the particular incident angle, the intensity of reflected light is rapidly decreased. Thus, by detecting the incident angle where the intensity of the reflected light is rapidly decreased, the wave number of the surface plasmon is determined and the physical properties of the specimen to be examined can be analyzed.
As the specimen analyzer utilizing the occurrence of the surface plasmon, a device set forth in Japanese Patent Kokai No. 2005-337940 is disclosed.
The specimen analyzer of Kokai No. 2005-337940, as shown in FIG. 1, is constructed with a light source section, a lens 55, a transparent substrate 56, and a photodetector 58. The light source section has a laser light irradiating device 51, an optical fiber 52, a collimation lens 53, and a strip-shaped aperture (not shown) provided to a mirror 54. In Kokai No. 2005-337940, parallel light P1 from the light source section is converted into convergent light through the lens 55. On the opposite surface of the transparent substrate 56 on which a specimen (not shown) is placed, a metal film 57 is deposited. The surface of the metal film 57 is irradiated with the convergent light. Totally reflected light is collected through the lens 55. The collected light is converted into parallel light P2 that travels in a direction opposite to that of the parallel light from the light source section and is detected by the photodetector 58.
In the conventional specimen analyzer, like that of Kokai No. 2005-337940, the parallel light from the light source section has been converted into convergent light through the lens when an examination position is irradiated with the light.